Yes, virtually everyone has antibodies still in their body from the recovery from prior ANY kind of coronavirus infection and/or bacterial respiratory infection. Everyone. The PCR test was abandoned because it was never effective in separating specific antibodies to a specific virus. Nor will any one test for whatever is coming through the window, differentiate (without massively expensive multi type testing). All that is needed is prevention as best can be done vs. any coronavirus S-Protein uptake by the ACE2 receptors on the cells lining the lungs— the method of infection of all coronaviruses. Since known since 1965.
The comedic aspect of the entire situation is that it has been known for years that coronavirus vaccines don’t work. The virus mutates that quickly. I think it was in the ‘60’s and ‘70’s that dogs were vaccinated against cv, but they eventually discontinued them because they aren’t effective.